The present invention is related generally to medical devices. More specifically, the present invention is related to catheters. The present invention includes apparatus and methods for affixing catheter tips to stent delivery catheters after a self-expanding stent has been loaded onto the catheter.
Heart attacks are a leading cause of death in the industrialized world, particularly in the United States. Many heart attacks are caused in part by a narrowed, stenosed coronary blood vessel. A medical procedure commonly used to deal with coronary vessel stenoses is angioplasty. Angioplasty, in particular Percutaneous Transluminal Coronary Angioplasty (PTCA), includes inserting a balloon catheter into the femoral artery near the groin, and advancing the catheter over the aortic arch and into a coronary artery. The balloon can be advanced through the coronary artery to the stenosis and inflated to widen or dilate the narrowed region. The balloon catheter can then be withdrawn. In some cases, the widened coronary vessel rebounds or re-closes, narrowing the vessel over a period of time.
Stents have come into increasing use to prevent the widened vessel regions from narrowing after angioplasty. A stent, typically having a tubular shape, can be put in place in the widened vessel region to hold the vessel walls apart and the lumen open in the event the vessel attempts to narrow again. One class of stents requires that the stent be forcibly outwardly expanded to put the stent into position against the vessel walls. Another class of stents, self-expanding stents, can be delivered to a site in a compressed or constrained configuration and released in the vessel region to be supported. The self-expanding stent then expands in place to a configuration having a wide lumen, typically pressing firmly against the vessel walls where released. The stent is commonly placed at a recently dilated, stenosed vessel region.
Self-expanding stents can be delivered to a target site mounted over an inner tube or shaft and constrained within the distal end of an enclosing retractable tube or sleeve. The self-expanding stent can be freed from the restraint of the outer sheath by either distally pushing the inner shaft against the stent or proximally pulling the retractable outer sheath from over the stent. Once free of the outer restraint, the self-expanding stent can expand to force itself against the vessel inner walls. Self-expanding stents are often elastically biased to assume an original larger shape after being temporarily compressed into a smaller size to more easily be transported through blood vessels to the target site.
Preferably, the stent is only temporarily compressed within a retractable sheath and compressed for a limited time. The exact size of the stent to be delivered may not be known until the patient is in the operating or treatment room of a hospital. In general, a catheter should have a maximum radial extent or profile no larger than necessary, in part to enable the catheter to reach further into narrower vessel regions. A self-expanding stent is most easily loaded in a proximal direction onto a catheter by compressing the stent and sliding the stent co-axially over the inner shaft distal end and within the retractable outer sheath. The stent must thus typically be slid over the catheter distal tip. The distal tip is optimally tapered, having a proximal width about the same as the width of the outer sheath, to provide a smooth transition from the distal tip to the outer sheath. This can present a situation where the compressed stent has an inner diameter too small to be advanced over the larger outer diameter distal tip of the catheter.
What would be desirable is a delivery catheter and method which would ease loading of a self-expanding stent by not having the tip on the delivery system at the time of loading. This would allow the self-expanding stent to be slid under the sheath with subsequent tip attachment.
The present invention includes a loaded, self-expanding stent delivery catheter assembly having an inner shaft or tube, a retractable sheath disposed over the inner shaft, and a compressed, self-expanding stent disposed co-axially between the inner shaft and retractable sheath. The inner shaft is a solid shaft in some embodiments, and a hollow shaft or tube having at least one lumen therethrough in other embodiments. The inner shaft terminates distally in a tip, preferably tapered, which can have a profile sufficiently large, such that the compressed stent cannot be passed proximally over the distal tip when mounted on the catheter distal end. The catheter assembly includes a distal tip adapted to be easily secured to the inner shaft after the stent has been proximally loaded over the catheter distal end. The present invention also allows attachment of catheter tips to tubes even after the tubes have been coated with material which are incompatible with later adhesive use.
One catheter includes a shrinkable film secured to the catheter inner shaft distal end and having a sufficiently small profile when collapsed or pressed against the inner shaft to allow the stent to be passed over the film, and onto the catheter distal region. After the stent is loaded, the tip is added by co-axially sliding a preformed conical tip over the inner shaft and under the shrinkable film and securing the tip to the inner shaft by shrinking the film over the tip and inner shaft. One embodiment utilizes heat-shrinkable film. One embodiment secures the film proximally to the inner shaft with outwardly projecting barbs or ridges. Another embodiment bonds the shrinkable film to the inner shaft.
In one set of embodiments, the distal tip has a proximal region allowing outward projections from the inner shaft to extend and cut into the region wall and secure the tip to the inner shaft. In some embodiments, the proximal region wall is sufficiently elastic to allow the proximal region to expand and contract when passed over the projections. In some embodiments, the proximal region is swollen with solvent to pass over the projections and the solvent later flashed off. In some embodiments, the proximal region wall has internal recesses or channels partially through the wall to receive outward projections from the inner shaft. In other embodiments the wall has holes or slots entirely through the wall. The proximal region holes or slots can be used to secure the tip to the inner shaft by allowing outward projections to fit through the openings, inhibiting the distal tip from moving relative to the inner shaft.
One catheter distal region according the present invention has a first configuration as a distal sleeve or tube, allowing a compressed stent to be passed over the tube. The tube can then be formed into a catheter distal tip by heating and reforming the tube material into a tip such as a conical tip having a lumen therethrough. One distal tip includes a proximal threaded region adapted to be threadably secured to a corresponding distal threaded region on the inner shaft. Another distal tip includes a proximal coil adapted to secure the tip to a corresponding distal threaded region on the inner shaft.
One group of distal tips according to the present invention is already attached to the inner shaft, but in a compressed or low profile state, and expands radially after a compressed stent has been passed proximally over the tip. One distal tip is formed of a reversibly compressible material which can be constricted by a compression tube while the stent is passed over the tube and allowed to expand to a larger profile by removing the compression tube. Another distal tip is formed of a swellable material which is chemically swollen to a larger outside diameter after a stent is allowed to pass over the tip and onto the distal region of the inner shaft. One suitable tip material is water-swellable and the tip is hydrated after the stent is in place.